- Diagnostic Procedure

SYSTEM DIAGNOSIS
The PCM uses information from the MAP and coolant sensors in addition to RPM to calculate spark advance as follows:

- Low MAP output voltage = More spark advance.
- Cold engine = More spark advance.
- High MAP output voltage = Less spark advance.
- Hot engine = Less spark advance.

Therefore, a low MAP output or a high resistance in the coolant sensor circuit could cause the detonation. A high MAP output or a low resistance in the coolant sensor circuit could cause poor pertormance.

IGNITION CONTROL (IC)
This system uses similar circuits between the ICM and the PCM that a distnbutor type system uses. Following is a brief description of the IC circuit. The PCM sends the Ignition Control (IC) pulses to the 1CM on the ignition control A & B. The signals are similar to the 7x reference pules square wave except that the PCM uses the sensors inputs to determine the pules timing to control spark advance. When the PCM receives the 7x reference signal, the PCM determines which pair of cylinders to fire 1 and 4 or 2 and 3.

SETTING TIMING
Because the reluctor wheel is a precision machined part of the crankshaft and the Crankshaft Position (CKP) sensor is mounted in an accurately located, fixed position, timing adjustment is not possible or necessary.